The present invention relates to magnetizing apparatus and magnetizing method for a magnetized pulser ring, as well as to a magnetized pulser ring.
Conventionally, rolling bearing units for rotatably supporting automobile wheels to a suspension system have been known in various structures. Among those rolling bearing units, there is one equipped with a rotational speed detecting device for detecting the rotational speed of wheels in order to control an antilock brake system (hereinafter, referred to as ABS) or traction control system (hereinafter, referred to as TCS).
Like this, the rotational speed detecting device to be incorporated in a rolling bearing unit includes a magnetized pulser ring which rotates along with the wheels, and a rotational speed sensor which outputs an output signal that varies at a frequency proportional to the rotational speed of the magnetized pulser ring (see Japanese Patent Laid-Open Publication HEI 10-115628).
The magnetized pulser rings are grouped in axial magnetization type and radial magnetization type. This radial-magnetization type magnetized pulser ring includes, as shown in FIG. 2, a cylindrical steel plate 21, and a cylindrical elastic magnetic member 22 provided over the entire periphery of the inner peripheral surface of the cylindrical steel plate 21.
Conventionally, there have been provided magnetizing apparatuses for radial-magnetization type magnetized pulser rings, which have a magnetizing yoke 23 having a cylindrical surface whose outer diameter is smaller than the inner diameter of the cylindrical elastic magnetic member 22, so that the magnetizing yoke 23 is made easier to insert into the cylindrical steel plate 21. Although not shown, N-pole areas and S-pole areas are alternately provided over the entire circumference on the outer periphery of the magnetizing yoke 23.
With the magnetizing apparatus of this construction, the magnetizing yoke 23 having a cylindrical surface is inserted into the cylindrical steel plate 21 so that the magnetizing yoke 23 is radially opposed to the cylindrical elastic magnetic member 22, thus achieving the magnetization of the cylindrical elastic magnetic member 22. As a result of this, N-pole areas and S-pole areas are alternately formed over the entire circumferential periphery of the cylindrical elastic magnetic member 22.
However, according to this conventional magnetizing apparatus for a magnetized pulser ring, because the outer circumferential surface of the magnetizing yoke 23 is a circumferential surface having a diameter smaller than the inner diameter of the cylindrical elastic magnetic member 22, there would occur a gap D between the magnetizing yoke 23 and the cylindrical elastic magnetic member 22 in performing the magnetization of the cylindrical elastic magnetic member 22. This would cause defect that the cylindrical elastic magnetic member 22 can be magnetized only to about 80% of a target magnetic force. For example, using the cylindrical elastic magnetic member 22 of such a weak magnetic force in an ABS-use rotational speed detecting device would cause the output signal of the rotational speed detecting device to become unstable.
Also, since the outer diameter of the cylindrical surface of the magnetizing yoke 23 is smaller than the inner diameter of the cylindrical elastic magnetic member 22, the magnetizing yoke 23 is more likely to be decentered with respect to the cylindrical elastic magnetic member 22. This causes a defect that the centering of the magnetizing yoke 23 with respect to the cylindrical elastic magnetic member 22 is difficult to achieve.
Accordingly, an object of the present invention is to provide magnetizing apparatus and magnetizing method for a magnetized pulser ring, as well as to a magnetized pulser ring, by which the magnetic force to which the cylindrical elastic magnetic member is magnetized can be enhanced, and yet in which the centering of the magnetizing yoke is easy to achieve.
In order to achieve the above object, there is provided a magnetizing apparatus for a magnetized pulser ring, in which a magnetizing portion of a magnetizing yoke is radially opposed to a cylindrical elastic magnetic member provided on a circumferential surface of a cylindrical steel plate so that magnetic-pole areas of opposite polarities are alternately formed circumferentially on the cylindrical elastic magnetic member, wherein:
the magnetizing portion is a conical surface slightly tilted with respect to an axis of the magnetizing yoke.
With this magnetizing apparatus for a magnetized pulser ring, for magnetization of the cylindrical elastic magnetic member, the magnetizing yoke is inserted into the cylindrical steel plate so that the magnetizing portion of the magnetizing yoke is radially opposed to the cylindrical elastic magnetic member. In this operation, when the magnetizing portion of the magnetizing yoke is brought into close contact with at least an axial end portion of the cylindrical elastic magnetic member, the magnetizing yoke becomes in its entire circumference close to or in contact with the cylindrical elastic magnetic member, because the magnetizing portion is a conical surface slightly tilted with respect to the axis. Accordingly, the magnetic force to which the cylindrical elastic magnetic member is magnetized can be enhanced. That is, the cylindrical elastic magnetic member can be magnetized sufficiently and reliably.
Also, because the magnetizing portion of the magnetizing yoke is a conical surface slightly tilted with respect to the axis, bringing the magnetizing portion of the magnetizing yoke into close contact with at least an axial end portion of the cylindrical elastic magnetic member makes the cylindrical elastic magnetic member and the magnetizing yoke concentric with each other. Accordingly, the magnetizing yoke can be centered with respect to the cylindrical elastic magnetic member easily and reliably.
Also, because the magnetizing portion of the magnetizing yoke is a conical surface tilted with respect to the axis, the insertion of the magnetizing yoke into the cylindrical steel plate can also be achieved easily.
In an embodiment, the conical surface which is the magnetizing portion is a convex surface, whereby the cylindrical elastic magnetic member is magnetized from an inner circumferential surface side of the cylindrical elastic magnetic member provided on an inner circumferential surface of the cylindrical steel plate.
With the magnetizing apparatus for a magnetized pulser ring in this embodiment, because the conical surface, i.e., the magnetizing portion of the magnetizing yoke is a convex surface, the cylindrical elastic magnetic member provided on the inner circumferential surface of the cylindrical steel plate can easily be magnetized from its inner circumferential surface side.
In an embodiment, the conical surface which is the magnetizing portion is a concave surface, whereby the cylindrical elastic magnetic member is magnetized from an outer circumferential surface side of the cylindrical elastic magnetic member provided on an outer circumferential surface of the cylindrical steel plate.
With the magnetizing apparatus for a magnetized pulser ring in this embodiment, because the conical surface of the magnetizing portion of the magnetizing yoke is a concave surface, the cylindrical elastic magnetic member provided on the outer circumferential surface of the cylindrical steel plate can be magnetized easily from its outer circumferential surface side.
A magnetizing method for a magnetized pulser ring of the present invention comprises the step of bringing the conical surface which is the magnetizing portion of the magnetizing apparatus for a magnetized pulser ring into close contact with at least an axial end portion of the cylindrical elastic magnetic member, thereby allowing the cylindrical elastic magnetic member to be magnetized.
According to the magnetizing method for a magnetized pulser ring, the magnetizing yoke is inserted into the cylindrical steel plate so that the conical surface, i.e., the magnetizing portion is brought into close contact with at least an axial end portion of the cylindrical elastic magnetic member. Then, the magnetizing yoke becomes in its entire circumference close to or in contact with the cylindrical elastic magnetic member, because the magnetizing portion of the magnetizing yoke is a conical surface slightly tilted with respect to the axis. Accordingly, the magnetic force to which the cylindrical elastic magnetic member is magnetized can be enhanced. That is, the cylindrical elastic magnetic member can be magnetized sufficiently and reliably.
Also, when the magnetizing portion of the magnetizing yoke is brought into close contact with at least an axial end portion of the cylindrical elastic magnetic member, the cylindrical elastic magnetic member and the magnetizing yoke become concentric with each other, because the magnetizing portion of the magnetizing yoke is a conical surface slightly tilted with respect to the axis. Accordingly, the magnetizing yoke can be centered with respect to the cylindrical elastic magnetic member easily and reliably.
The present invention also provides a magnetized pulser ring comprising a cylindrical steel plate, and a cylindrical elastic magnetic member provided on a circumferential surface of the cylindrical steel plate, wherein
magnetic force of one axial end portion of the cylindrical elastic magnetic member is stronger than magnetic force of the other axial end portion of the cylindrical elastic magnetic member, and
magnetic force of the cylindrical elastic magnetic member is generally uniform along its circumferential direction.
The magnetized pulser ring of the invention can be manufactured with the use of the magnetizing apparatus or the magnetizing method as described above. Accordingly, this magnetized pulser ring has an advantage that the magnetic force is strong and does not vary in the circumferential direction, because the magnetized pulser ring is magnetized in a centered state by the magnetizing apparatus.